Concentrating on the nature of anion and proton transport in the intact turtle bladder and in isolated apical membrane vesicles of these epithelial cells, we intend to evaluate the nature of the electrical response across each plasma membrane (by microelectrode impalements) as well as that across the epithelial cell to imposed changes in the extra-cellular chloride concentration (while the concomitant reabsorption of bicarbonate is kept constant at a maximal level and while the concomitant reabsorption by bicarbonate is kept constant at a zero level). We also intend to evaluate the corresponding electrical responses to metabolically-initiated (N2 to O2) chloride transport (while HCO3 reabsorption is fixed at a zero level). An electrogenic type of chloride reabsorption should respond electrically, by an increased PDor ISC, to any of these maneuvers; an electroneutral Cl:HCO3 exchange process should respond in an electrically-silent manner. Using free-flow electrophoresis and lectin-affinity chromatography, we plan to obtain inside-out apical membrane vesicles of these epithelial cells and to evaluate the electrogenic or electroneutral nature of the individual ion transport processes - (i.e., chloride reabsorption, bicarbonate reabsorption, bicarbonate secretion and proton secretion). The replication and characterization of any imn transport in these vesicles would be contrued as confirmatory evidence for the existence and for the type of transport process inthe intact epithelium. In order to measure the transmembrane potentials, the ion gradients, and the internal pH in these vesicles, we shall use trace quantities of radiolabelled lipophilic cations (tetraphenyl phosphonium) or anions (tetraphenyl borane); 36Cl, 22Na, 35SO4, H14CO3; and radiolabelled weak acids (DMO) or weak alkalis (aminopyrine).